The filter elements are often made of a ceramic material and have a plurality of inlet channels and outlet channels running parallel to each other.
Filter elements made of ceramic materials are manufactured by extrusion. This means that the blank of the filter element is a prismatic body having a plurality of channels running parallel to each other. The channels of a blank are initially open at both ends.
For the exhaust gas to be purified to flow through the walls of the filter, part of the channels is closed at the downstream end of the filter element, while another part of the channels is closed at the upstream end of the filter element. Two groups of channels are thus formed, namely the so-called inlet channels, which are closed at their downstream ends, and the so-called outlet channels, which are closed at the upstream ends of the filter element.
A flow connection exists between the inlet channels and the outlet channels only through the porous walls of the filter element, so that the exhaust gas may only flow through the filter element by flowing from the inlet channels through the walls of the filter element into the outlet channels.
In order to ensure an optimally effective operation of the filter element, a most uniform temperature distribution possible over the cross section of the filter element during the operation of the internal combustion engine is strived after.